#define _CRT_SECURE_NO_WARNINGS 1

//https://leetcode.cn/problems/number-of-islands/

class Solution {
    typedef pair<int, int> PII;
    int dx[4] = { 0, 0, 1, -1 };
    int dy[4] = { 1, -1, 0, 0 };
    vector<vector<bool>> vis;
    int m, n;

public:
    void bfs(vector<vector<char>>& grid, int i, int j) {
        queue<PII> q;
        q.push({ i, j });
        vis[i][j] = true;
        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int z = 0; z < 4; z++)
            {
                int x = a + dx[z], y = b + dy[z];
                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && vis[x][y] == false)
                {
                    q.push({ x, y });
                    vis[x][y] = true;
                }
            }
        }
    }

    int numIslands(vector<vector<char>>& grid) {
        m = grid.size(), n = grid[0].size();
        vis.resize(m, vector<bool>(n));
        int ret = 0;

        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == '1' && vis[i][j] == false) {
                    ret++;
                    bfs(grid, i, j);
                }
            }
        }
        return ret;
    }
};